Starting and operating circuit for arc discharge device



Dec. 26, 1961 J POPA 3,015,058 STARTING AND OPERATING CIRCUIT FOR ARCDISCHARGE DEVICE Filed March 3, 1958 l/MMP .7- [ZAHP V l I fin/e1? tor:JO/Zl? papa,

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United States Patent 3,015,058 STARTING AND OPERATING CIRCUIT FOR ARCDISCHARGE DEVICE John Popa, Fort Wayne, Ind., assignor to GeneralElectric Company, a corporation of New York Filed Mar. 3, 1958, Ser. No.718,799 7 Claims. (Cl. 323-60) This invention relates to circuits forstarting and operating arc discharge devices, such as mercury vaporlamps, and more particularly to a starting and operating circuit forsuch devices with provision for selectively varying the wattage and inturn the light output of the device.

All are discharge devices, such as mercury vapor and fluorescent lamps,possess an inherent negative resistance characteristic, i.e., theirresistance decreases as the current flow therethrough increases. It isthus necessary to provide a high initial or open circuit voltage inorder to strike the arc, i.e., to start the device, however, if thisopen circuit voltage were thereafter maintained, the device wouldrapidly destroy itself by virtue of the increasing current flow due toits negative resistance characteristic. It is thus additionallynecessary to provide means for limiting the current flow to the arcdischarge device after the device has started, such current limitationconventionally being referred to as ball-asting. A loose coupled or highreactance transformer has been commonly employed for performing bothstarting and ballasting functions for are discharge devices operating onalternating current, such transformers being admirably suited for thepurpose since they provide a high secondary open circuit voltage whichimmediately falls to a much lower level after the arc discharge devicehas started and load current begins to flow. Such circuits are commonlyreferred to as lagging current circuits since the system is highlyinductive; these circuits have had the recognized disadvantage ofproviding low line power factor and also relatively poor regulation oflamp current, and thus in turn wattage and light, output responsive toline voltage variations.

The low line power factor and poor regulation characteristics of thehigh reactance lagging current ballast circuit have been overcome by thecommon use in recent years of the so-called high reactance-lead circuitin which a capacitor proportioned to draw leading current is seriallyconnected between the secondary winding of the high reactancetransformer and the arc discharge device. In such a circuit and with atransformer designed for normal flux densities, the leading currentdrawn by the capacitor causes an increase in the secondary voltage ofthe transformer thus in turn tending to cause saturation of thetransformer core in the region of the secondary winding; operation ofthe secondary portion of the core about the knee of its saturation curvecauses the transformer to function in the manner of a non-linear reactorthus providing greatly improved regulation of lamp current responsive toline voltage changes, such a circuit further providing much higher linepower factor than is provided by conventional high reactance-lagcircuits. In such high reactance-lead ballast circuits after the aredischarge device has operated long enough to develop full voltage acrossitself, it can be safely assumed that the transformer secondary terminalvoltage is the vector sum of the voltage across the device and thevoltage across the capacitor. Since, by virtue of its negativeresistance characteristic, the voltage across the device is essentiallyconstant regardless of the current flow therethrough, and since thesecondary terminal voltage under load is dependent upon the loadcurrent, it is seen that the only variable remaining is the capacitorvoltage. Thus, in such circuits, ti is customary to adjust the arcdischarge 3,015,058 Patented Dec. 26, 1961 device current to its desiredor rated value by suitable selection of the value of the capacitor.

In the particular case of arc discharge lamps, such as mercury vaporlamps, while a fixed value of lamp current and thus lamp wattage andlight output, is generally desired, there are instances in which it isdesired to operate a given lamp at more than one level of light outputor to provide selectively variable light output, i.e., generallyreferred to as dimming action. While operation of the lamp at twodifferent light output levels may be secured by the provision of twocapacitors having respectively different values of capacitance with aselector switch for selecting one or the other capacitor, the capacitorsemployed in such circuits are expensive and further, such an arrangementprovides only two light output levels; provision of a plurality ofcapacitors to provide corresponding plurality of light output levels isprohibitively expensive and still does not provide continuously variabledirnming action. Energization of the primary winding of the highreactance lagging current transformer through a variable voltageautotransformer has also been proposed, however, such an arrangement hasa deleterious effect on the line power factor and further, theadjustment of the autotransformer to provide a low primary voltage mayin turn reduce the secondary open circuit voltage to a point where thelamp will not fire. It is therefore desirable to provide a highreactance lead ballast circuit with means for varying the current of thearc discharge device operated thereby which does not require the use ofmore than one capacitor nor have the disadvantages of a variable voltageautotransformer connected between the source of alternating current andthe primary winding.

It is therefore an object of my invention to provide an improved circuitfor starting and operating arc discharge devices having provision forvaryng the current of the device after it has started.

Another object of my invention is to provide a ballast circuit of thehigh reactance-lead type for are discharge devices with improved meansfor varying the current of the device after it has started.

A further object of my invention is to provide a ballast circuit of thehigh reactance-lead type for are discharge devices with means forselectively varying the current of the device after it has started andwhich does not possess the disadvantages of the applicant.

My invention in its broader aspects provides a high reactancetransformer having its primary winding adapted to be connected to asource of alternatng current and having a capacitor and a source ofselectively variable voltage serially connecting the secondary windingof the transformer across the arc discharge device. In the preferredembodiment of my invention, I provide an additional low reactancetransformer having its secondary winding connected in series with thecapacitor and having its primary winding energized from a variablevoltage autotransformer. In this manner, a voltage which may be eitherbucking or boosting with respect to the capacitor voltage is providedthereby effectively to vary the capacitor voltage and thus in turn thecurrent of the arc discharge device.

Further objects and advantages of my' invention will become apparent byreference to the following description and the accompanying drawing, andthe features of novelty which characterize this invention will bepointed out with particularity in the claims annexed to and forming apart of this specification.

In the drawing,

FIG. 1 is a schematic diagram showing a starting and operating circuitincorporating my invention for an arc discharge lamp, and

prior circuits known to acispss FIG. 2 is a vector diagram useful inexplaining the mode of operation of the circuit of FIG. 1.

Referring now to FIG. 1, my improved circuit, generally identified as 1,is shown here connected for starting and operation of an arc dischargelamp 2, as for example a 400 watt mercury vapor lamp. A conventionalhigh reactance transformer T is provided having a core, schematicallyshown at 3, with a primary winding 4 connected across line terminals 5,which in turn are adapted to be connected to a suitable source ofalternating current (not shown), such as 115 volts, 60 cycles. Asecondary winding 6 is provided on the core 3 loosely coupled to theprimary winding 4, for example by being spaced from the primary windingby means of magnetic shunts, shown schematically at 7, as is well knownin the art; it will be understood that the specific high reactancetransformer T does not form a part of my invention and that anyconventional high reactance transformer construction may be utilized inmy improved circuit.

A pair of output terminals 8 and 9 are provided adapted to have the arcdischarge lamp 2 connected thereacross. One end 10 of the secondarywinding 6 of high reactance transformer T is directly connected tooutput terminal 9 while the other end 11 is serially connected to theother output terminal 8 by a suitable capacitor 12 and secondary winding13 of low reactance transformer T The primary winding 14 of transformerT has one side 15 connected to one side 16 of Winding 17 of a suitablevariable autotransformer 18, the other side 19 of primary winding 14 oflow reactance transformer T being connected to the selectivelyadjustable tap 20 of the variable voltage autotransformer 18. The inputterminals 16 and 21 of variable voltage autotransformer 18 are shownhere as being connected across input terminals 5, however, it will bereadily understood that they may be separately connected forenergization from another suitable source of alternating current.

It will now be seen that by means of the variable voltageautotransformer 18 and the low reactance transformer T having itssecondary winding 13 connected in series with capacitor 12, an inductiveelement has been added in series with the capacitor 12 in such a mannerthat the inductive element provides a continuously variable voltagewhich may be made either to buck or boost the capacitor voltage.Referring now to FIG. 2, there is shown a vector diagram which closelyapproximates the conditions in the circuit of FIG. 1 after lamp 2 hasfired and come up to voltage, and with the voltage induced in secondarywinding 13 of low reactance transformer T bucking the capacitor voltage.Since the arc discharge lamp 2 is essentially a resistive device, itscurrent flow after starting, identified as L is in phase with thevoltage developed thereacross, i.e., across output terminals 8 and 9,identified as V The capacitor voltage, identified as V naturally lagsthe lamp voltage and current by 90", as shown, with the voltage inducedin the secondary winding 13 of low reactance transformer T identified asV leading the lamp voltage and current by 90, as shown. It will now beseen that since the voltage VTzsw opposed or bucks the capacitor voltageV the resulting voltage between end 11 of the secondary winding 6 ofhigh reactance transformer T and output terminal 8 is the numericaldifference of the two, i.e., V -V this voltage being vectoriallyresolved with the lamp voltage V to provide the secondary windingterminal voltage under load, identified as V which in turn vectoriallyequals V -j(V -t-V j. It will now be readily seen that adjustment of theadjustable tap 20 on the variable voltage autotransformer 18 will inturn vary the voltage V and thus in turn vary the terminal voltage ofsecondary winding 6 of transformer T and thus the lamp current. It willalso be readily understood, however, that the connections of the lowreactance transformer T may be reversed so that the voltage induced inthe secondary winding 13 boosts rather than bucks the voltage acrosscapacitor 12.

A circuit has been constructed in accordance with FIG. 1 for operationof a 400 watt mercury vapor lamp. In this system, primary winding 4 oftransformer T had 196 turns of .07 63 inch diameter wire, secondarywinding 6 had 4 62 turns of .0605 inch diameter wire, and thus providedan open circuit voltage of 253 volts with primary winding 4 connected toa source of volts, 60 cycles. Capacitor 12 had a capacitance of 20.9rnicrofarads, transformer T had its primary winding 14 having 4-40 turnsof .0302 inch diameter wire and secondary winding 13 having 227 turns of.0453 inch diameter wire. Variable voltage autotransformer with itsinput terminals 16 and 21 connected across the input terminals 5provided a selectively variable voltagebetween 0 and 214- volts. Withthis arrangement and the variable voltage autotransformer 18 adjusted toprovide full wattage operation of lamp 2, i.e., 400 watts, the measuredvoltage appearing across the secondary winding 6 of transformer T was420 volts and the voltage appearing across capacitor 12 was 400 volts,the voltage appearing across secondary winding 13 of transformer T waszero, the lamp voltage was 134 volts, and the lamp current 3.24 amps,When the lamp wattage of the circuit was reduced 50% in a continuouslyvariable fashion to 200 watts, it was found that the measured secondaryvoltage of transformer T was 320 volts, the capacitor voltage was 213volts, the voltage appearing across the secondary winding 13 oftransformer T was 115 volts, the lamp voltage was 112.5 volts, the lampcurrent was 1.97 amps.

It will now be seen that I have provided an improved starting andoperating circuit for arc discharge devices,- particularly arc dischargelamps, in which the lamp current and thus in turn lamp wattage and lightoutput may be continuously varied, either upwards or downwards from areference level, without requiring the use of capacitor banks, or thedisadvantages of the energization of the primary winding of the highreactancc transformer through a variable voltage autotransformer.

While I have illustrated and described a specific em bodiment of thisinvention, further modifications and im provements will occur to thoseskilled in the art and I desire that it be understood therefore thatthis invention is not limited to the specific form shown and I intend inthe appended claims to cover all modifications which do not depart fromthe spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A starting and operating circuit for an arc discharge devicecomprising: a high reactance transformer having a primary windin adaptedto be connected to a source of alternating current and having asecondary winding; a pair of output terminals adapted to be connected tosaid arc discharge device; and a capacitor and a source of selectivelyvariable voltage serially connected with said secondary winding acrosssadi output terminals, said voltage of said selectively variable sourcebeing in bucking relationship with the voltage of said capacitor.

2. A starting and operating circuit for an arc discharge devicecomprising: a high reactance transformer having a primary windingadapted to be connected to a source of alternating current and having asecondary winding; a pair of output terminals adapted to be connected tosaid are discharge device; a capacitor; and inductive means providing aselectively variable voltage serially connected with said capacitor andsaid secondary winding across said output terminals, said selectivelyvariable voltage being in opposing relationship with the voltage of saidcapacitor.

3. A starting and operating circuit for an arc discharge devicecomprising: a high reactance transformer having a primary windingadapted to be connected to a source of alternating current and having asecondary winding; a pair of output terminals adapted to be connected tosaid arc discharge device; a capacitor; and a second transformer havingits secondary winding serially connected with said capacitor and saidhigh reactance transformer secondary winding across said outputterminals and having .its primary winding adapted to be connected to aselectively variable source of alternating current voltage for varyingthe secondary voltage thereof thereby to vary the voltage of said aredischarge device, said secondary voltage of said second transformerbeing in bucking relationship with the voltage of said capacitor.

4. A starting and operating circuit for an arc discharge devicecomprising: a high reactance transformer having a primary windingadapted to be connected to a source of alternating current and having asecondary winding; a pair of output terminals adapted to be connected tosaid are discharge device; a capacitor; 'a second transformer having aprimary winding and a secondary Winding serially connected with saidcapacitor and said high reactance transformer secondary winding acrosssaid output terminals, said capacitor being proportioned to draw leadingcurrent through said high reactance transformer secondary Winding; andmeans connected to said other transformer primary winding forselectively varying the secondary voltage thereof thereby to vary thevoltage of said arc discharge device.

5. A starting and operating circuit for an arc discharge devicecomprising: a high reactance transformer having a primary windingadapted to be connected to a source of alternating current and having asecondary winding; a pair of output terminals adapted to be connected tosaid are discharge device; a capacitor; a low reactance transformerhaving a primary winding and a secondary winding serially connected withsaid capacitor and said high reactance transformer secondary windingacross said output terminals, said capacitor being proportioned to drawleading current through said high reactance transformer secondarywinding; and means connected to said low reactance transformer primarywinding for selectively varying the secondary voltage thereof thereby tovary the voltage of said are discharge device, said secondary voltage ofsaid low reactance transformer being in bucking relationship with thevoltage of said capacitor.

6. A starting and operating circuit for an are discharge devicecomprising: a high reactance transformer having a primary windingadapted to be connected to a source of alternating current and having asecondary winding; a pair of output terminals adapted to be connected tosaid are discharge device; a capacitor; a low reactance transformerhaving a primary winding and a secondary winding serially connected withsaid capacitor and said high reactance transformer secondary windingacross said output terminals, said capacitor being proportioned to drawleading current through said high reactance transformer secondarywinding; and a variable voltage 'autotransformer connected to said lowreactance transformer primary winding and adapted to be connected to asource of alternating current for selectively varying the secondaryvoltage of said low reactance transformer thereby to vary the voltage ofsaid are discharge device.

7. A starting and operating circuit for an arc discharge devicecomprising: a high reactance transformer having a primary windingadapted to be connected to a source of alternating current and having asecondary Winding; a pair of output terminals adapted to be connected tosaid arc discharge device; a capacitor; a low reactance transformerhaving a primary winding and a secondary winding serially connected withsaid capacitor and said high reactance transformer secondary windingacross said output terminals, said capacitor being proportioned to drawleading current through said high reactance transformer secondaryWinding; and a variable voltage autotransformer connected between saidlow reactance transformer primary winding and said high reactancetransformer primary winding for selectively varying the secondaryvoltage of said low reactance transformer thereby to vary the voltage ofsaid arc discharge device.

References Cited in the file of this patent UNITED STATES PATENTS687,147 Fleming Nov. 19, 1901 2,683,240 Strange July 6, 1954 2,774,917Passrnore Dec. 18, 1956 2,849,656 Karash Aug. 26, 1958 2,870,398 SolaJan. 20, 1959

